1. FIELD OF THE INVENTION
The present invention relates to a hydraulic booster device and particularly, to a hydraulic booster device for use in a brake system for vehicles.
2. DESCRIPTION OF THE PRIOR ART
There are conventionally known such hydraulic booster devices of a so-called strokeless type in which the stroke of an operating member is slight required only to open and close a hydraulic pressure control valve, and devices of a stroke type in which the stroke of an operating member is the same as that of an operating piston in a master cylinder, for example, as disclosed in Japanese Patent Publication No. 39953/78.
In a hydraulic booster device of the above strokeless type, however, there is a sense of incompatibility because the stroke of the operating member is slight and the amount of operation does not correspond to the amount of movement. In addition, when there is a falling of hydraulic pressure, the stroke increases, leading to a difficult layout of a seat of a hydraulic pressure control valve and so on. In a hydraulic booster device of the stroke type, the stoke of the operating member is too large. To shorten the stroke, the inside diameter of a cylinder body in the master cylinder may be increased, which causes the effectiveness to be deteriorated when there is a falling of hydraulic pressure.